On the subject of grapes/raisins and dogs health:
Go to the following web site - www.aspca.org/apcc
This is a site for the American S.P.C.A., specifically relating to poisons and pets. Near the bottom of the page is a link relating to grapes called "The wrath of grapes" written by Charlotte Means, D.V.M.
Although not conclusive (research is ongoing) it does shed some light on the subject.
Hope this helps.